The present invention relates to methods for characterizing various stimuli, for example touch inputs, using time domain differential sensing techniques.
Touch inputs are widely used as an input methodology. For example, touch inputs are used in conjunction with appliances, tablets, and smartphones. Touch inputs are also used in conjunction with fingerprint sensors. For example, fingerprint swipe sensors can use conventional capacitive sensing techniques to convert a touch swipe into a two-dimensional image of a fingerprint. Handprint sensors are an extension of this technology, and can generate a pixelated image where each pixel includes a greyscale value proportional to the distance from the skin.
Touch inputs can be determined based on a capacitive output of an electrode. According to one known method, the value of the capacitive output is used to determine the presence of a touch input on a substrate, the location of a touch input on a two-dimensional panel, or the individual peaks and valleys in a fingerprint. However, the capacitive output is generally compared against a reference value, which in practice is an approximation. The reference value can lead to false touch inputs or the failure to register actual touch inputs depending on manufacturing tolerances, environmental changes, and other considerations.